Explosively actuated ground interrupting device

ABSTRACT

An explosively actuated ground interrupting device for a lightning arrester has an explosive charge which may be detonated by a resistor having a coil-shaped portion which presents a high impedance to transient currents, thereby inhibiting false detonation of the explosive charge.

United States Patent Irie et al.

[54] EXPLOSIVELY ACTUATED GROUND INTERRUPTING DEVICE [72] inventors: Kouhei lrie; Misao Kobayashi; Masaru Shlmamura, all of Shizuoka, Japan [73] Assignee: Kabushlki Keisha Meidensha, Tokyo,

Japan [22] Filed: June 3, 1970 [21] Appl. No.: 43,030

[30] Foreign Application Priority Data 1 51 June 6, 1972 2,629,765 2/1953 Cougnard ..313/325 X 3,328,632 6/1967 Robinson ..313/325 UX 3,501,667 3/1970 Melanson ..313/325 FOREIGN PATENTS OR APPLICATIONS 153,501 6/1962 U.S.S.R. ..313/325 Primary Examiner-John K. Corbin Assistant Examiner-Toby H. Kusmer Attorney-Kelman and Herman [57] ABSTRACT An explosively actuated ground interrupting device for a lightning arrester has an explosive charge which may be detonated by a resistor having a coil-shaped portion which presents a high impedance to transient currents, thereby inhibiting false detonation of the explosive charge.

8 Claims, 12 Drawing Figures PATENTEDJUN sma 3,688,458

. SHEET 10F 2 PATENTEnJun a ma SHEET 2 OF 2 FIG.3

FIGJ

FIG.5

FIG.6

EXPLOSIVELY ACTUATED GROUND INTERRUPIING DEVICE The present invention relates to a device for interrupting the earth or ground connection to a lightning arrester, thereby pennitting re-transmission of power after the occurrence of a grounding fault resulting from damage to the lightning arrester.

When a lightning arrester is damaged by operation beyond its working limits, re-transmission of power would be impossible due to grounding of the lightning arrester and a ground separating device is normally provided between the lightning arrester and ground. Thus, if the dynamic current is not interrupted by a defective lightning arrester, the ground connection is speedily interrupted. In recent years, ground separating devices have been required to have very high sensitivity.

In known ground separating devices heat generated in a resistor by the current flowing through the lightning arrester is utilized to detonate a charge of dynamite, thereby causing ground separation. With apparatus of this type, it is necessary to avoid malfunction caused by impulse currents and by the high sensitivity of the device. I

Accordingly, it has been proposed to provide a discharge gap outside the sealed vessel in which the resistor and the dynamite charge are housed, and most of the impulse current flows through the gap. When a large impulse current flows through the ground separating device, the'small part of the impulse current which still flows through the resistor may cause the dynamite to explode when a dynamic current flowing in the resistor exceeds, by even a small amount, the design value in a very sensitive ground interrupting device.

The discharge gap of known devices is exposed to the atmosphere, and its characteristics may change with time due to corrosion, dust, or other foreign material such as rain water.

A first object of the present invention is to provide a ground interrupting device having a high degree of sensitivity, yet free of the-afore-described shortcomings.

A second object of the present invention is to provide a ground interrupting device of small size at low cost which uses its component parts to perform multiple functions.

A third object of the present invention is to provide a ground interrupting device in which the discharging characteristics of the discharge gap are not affected by corrosion. With these objects in view, the invention provides'an im-' provement in a device for interrupting a ground connection for a" lightning arrester in which device conductors define a discharge gap, and a sealed vessel encloses a resistor arranged in parallel circuit with the gap and in thennal contact with a body of heat-sensitive explosive. According to the invention, theresistor has a coil-shaped portion.

IN THE ATTACHED DRAWING:

FIG. I shows a ground interrupting device of the invention in elevational section;

FIGS. 2a to 2f illustrate elements of the device of FIG. 1 in respective perspective views;

FIG. 3 shows another device of the invention in elevational section;

FIG. 4 is a perspective view of a terminal for use with devices of the invention;

FIG. 5 shows a modified cap for assembly with the tenninal of FIG. 4 in elevational section;

FIG. 6 illustrates the method of inserting the cap of FIG. 5 in the terminal of FIG. 4 in elevational section; and

FIG. 7 shows the assembled cap and terminal.

In the apparatus of FIGS. 1 and 2a to 2f, a tubular cylinder 1 of insulating material has an annular groove 2 axially centered in its outer circumference and bevels 3 on its two outer, circular edges. Two cup-shaped metal caps 4 are fitted over the two axial ends of the cylinder 1 .so that their rims spacedly face each other near the groove 2. An L-shaped terminal 5 is fixed to the outer bottom face of each cap 4.

The rim of each cap 4 is axially notched, and alternating rim segments 4a between-adjacent notches are bent into the groove 2 to secure the cap on the cylinder 1 The other rim segments 4b are bent slightly outward of the groove 2 and form a discharge gap g axially coextensive with the groove 2. Ring-shaped packings 6 are inserted between the inner surfaces of the caps 4 and the bevels 3 of the cylinder 1. They hold the segments 4a against the cylinder 1 and seal the axial bore 7 of the cylinder 1.

A resistor 8 which is partly coil-shaped and partly straight is enclosed in the bore 7. Its coil portion engages one cap, and the straight portion passes in direct thermal contact through an annular disc 9 of dynamite and through two soft insulating discs 10 on opposite faces of the'disc 9. The free end of the straight resistor portion is offset for contact with the lower cap 4 so that the caps 4 are connected in parallel circuit with the gap 3 by the series-connected, integral coil-shaped and straight portions of the resistor 8.

When a current impulse from a transmission line enters the non-illustrated associated lightning arrester, the high impedance of the coil-shaped portion of the resistor 8 causes the impulse to pass to ground between the terminals 5 through the gap g. During the subsequent dynamic stage, the impedance of the coil portion is low, and the dynamic current can flow through the resistor and heat the dynamite 9 without detonating the same if the insulation of the lightning arrester is quickly restored.

If the lightning arrester is damaged by operating beyond its design limits, the resulting fault current passing through the resistor 8 heats the latter after a few cycles sufficiently to explode the dynamite 9 whereby the lower cap 4 is blown ofi and the circuit between the lightning arrester and ground is interrupted.

Because of the partial coil shape of the resistor 8, the device can withstand relatively large impulse currents while being sensitive to dynamic current. This effect can be enhanced by inserting a magnetic core, not shown, into the coil-shaped resistor portion. The central, grooved segment of the cylinder 1 is relatively weak and is readily broken by the explosion.

The caps 4 function as sealing lids for the bore 7 and simultaneously constitute electrodes for the discharge gap 3. They also protect the cylinder 1 and the components arranged therein so that the device consists of only few and inexpensive parts and is easily assembled.

The modified device of the invention shown in FIG. 3 has an insulating cylinder 1 identical with that shown in FIG.'2c and enclosing a resistor 8 and dynamite charge 9 in its bore 7. The rim segments 4 of two caps 4 on opposite ends of the cylinder 1 are bent into the groove 2 of the cylinder 1 to secure the caps and to compress packing rings 6. Terminals 5 are attached to the caps 4.

A cover 11 of stainless steel having the shape of an inverted cup conformingly envelops the upper cap 4 and is fastened to the cap by a press fit or by adhesive. The tenninal 5 on the upper cap passes through a hole 12 in the cover 1 l. The lower portion of the cover 11 spacedly surrounds the lower cap 4 and carries a projection 13 on its inner surface to form a discharge gap g with the lower cap 4. The width of the gap may be set precisely by inserting a gage between the projection 13 and the lower cap 4 and thereafter suitably deforming the cover 1 l.

The cover 11 prevents deterioration of the discharge characteristics of the device by corrosion or by the deposition of dust or other foreign matter. The width of the gap can be set after the actual assembly operation which thereby becomes extremely easy.

FIGS. 4 to 7 illustrate a simple manner of attaching L- shaped terminals 5 to caps 4. The terminal 5 is formed with an aperture 14in one of its legs. The cap 4 has an outward, cylindrical projection 15 in its bottom surfaces which constitutes an integral hollow rivet dimensioned for insertion in the aperture 14. After insertion, the rivet I5 is deformed between an anvil l6 shaped to be received in the cap 4 and a die 17, as is shown in FIG. 6 to lock the rivet in the aperture 14, as is seen in FIG. 7.

The invention is not limited to the specifically described embodiments which may readily be modified without departing from the scope of the invention.

What is claimed is:

1. In a device for interrupting a ground connection for a lightning arrester, said device including conductive means defining a discharge gap, a sealed vessel, an elongated resistor mounted in said vessel in parallel circuit with said gap, and a body of heat-sensitive explosive in thermal contact with said resistor, the improvement whichcomprises a longitudinal portion of said resistor being coil-shaped.

2. In a device as set forth in claim 1, said resistor having a straight longitudinal portion, said straight portion being in thermal contact with said body of explosive.

3. In a device as set forth inclaim 1, said vessel including a body of insulating material formed with a bore, said resistor and said body of explosive being received in said bore, said conductive means including a substantially cup-shaped member closing one end of said bore in electrical contact with one end of said resistor, a rim portion of said cup-shaped member bounding said gap.

4. In a device as set forth in claim 3, said conductive means further including a substantially cup-shaped protective cover enveloping said body of insulating material in spaced relation to said rim portion and bounding said gap.

5. In a device as set forth in claim 1, said vessel including a 'a part of the rim portion of one of said cup-shaped members engaging said recess and thereby axially securing said one member on said cylindrical body.

7. In a device as set forth in claim 5, said cylindrical body being fonned with an annular groove in the outer circumference thereof, said groove being axially coextensive with said gap, and respective parts of said rim portions being received in said groove and thereby axially securing said cupshaped members on said cylindrical body.

8. In a device as set forth in claim 3, a terminal formed with an opening therein, the bottom portion of said cup-shaped member being formed with an integral hollow rivet extending through said opening and securing said terminal to said cupshaped member. 1 

1. In a device for interrupting a ground connection for a lightning arrester, said device including conductive means defining a discharge gap, a sealed vessel, an elongated resistor mounted in said vessel in parallel circuit with said gap, and a body of heat-sensitive explosive in thermal contact with said resistor, the improvement which comprises a longitudinal portion of said resistor being coil-shaped.
 2. In a device as set forth in claim 1, said resistor having a straight longitudinal portion, said straight portion being in thermal contact with said body of explosive.
 3. In a device as set forth in claim 1, said vessel including a body of insulating material formed with a bore, said resistor and said body of explosive being received in said bore, said conductive means including a substantially cup-shaped member closing one end of said bore in electrical contact with one end of said resistor, a rim portion of said cup-shaped member bounding said gap.
 4. In a device as set forth in claim 3, said conductive means further including a substantially cup-shaped protective cover enveloping said body of insulating material in spaced relation to said rim portion and bounding said gap.
 5. In a device as set forth in claim 1, said vessel including a substantially cylindrical body of insulating material formed with an axial bore therethrough, said resistor and said body of explosive being received in said bore, said conductive means including two substantially cup-shaped members enveloping respective axial ends of said cylindrical body and closing the axial ends of said bore, respective rim portions of said cup-shaped members being spaced to define said gap therebetween.
 6. In a device as set forth in claim 5, said cylindrical body being formed with a recess in the outer circumference thereof, a part of the rim portion of one of said cup-shaped members engaging said recess and thereby axially securing said one member on said cylindrical body.
 7. In a device as set forth in claim 5, said cylindrical body being formed with an annular groove in the outer circumference thereof, said groove being axially coextensive with said gap, and respective parts of said rim portions being received in said groove and thereby axially securing said cup-shaped members on said cylindrical body.
 8. In a device as set forth in claim 3, a terminal formed with an opening therein, the bottom portion of said cup-shaped member being formed with an integral hollow rivet extending through said opening and securing said terminal to said cup-shaped member. 